Protistology 5 (4) 256-267 (2008)
Choanoflagellate evolution: the morphological perspective*
Barry S.C. Leadbeater
School of Biological Sciences, University of Birmingham, Birmingham B15 2TT, UK
Summary
Choanoflagellates are a ubiquitous group of heterotrophic nanoflagellates found in aquatic environments everywhere. Recent molecular phylogeny has
confirmed them as being the sister group to the Metazoa. Tey are easily recognised by their spherical to ovoid cell with a single anterior flagellum surrounded
by a collar of microvilli. Choanoflagellates are filter feeders, the flagellum creating a flow of water from which food particles, mostly bacteria, are trapped on the
outside of the collar. To enhance the flow of water over the collar, the cell needs to be stationary and this is achieved by the production of an organic theca with
a stalk. Tecate choanoflagellates are common in both freshwater and marine environments but require a substratum for settlement. A group of exclusively marine
choanoflagellates, Acanthoecidae, has developed a siliceous basket-like covering, the lorica, that encloses the cell and serves not only to resist the locomotory
forces created by the flagellum but also to direct and enhance water flow over the collar. Variations in the morphology of the lorica, the amount of silicification and
the positioning of the inner organic investment have allowed loricate species to diversify and thereby inhabit many different microniches within the water column.
Key words: Choanoflagellate, glycocalyx, theca, lorica, siliceouscostae, waterflows, ecology, planktonic species, phylogeny
| Load PDF |
Back to Contents |
|